Systemic lupus erythematosus (SLE) is a chronic autoimmune disease that frequently causes widespread inflammation and serious organ damage. Recent studies have implicated toll-like receptors, particularly TLR9 in the pathogenesis of SLE. TLR9 ligands, such as bacterial DNA and synthetic CpG-oligonucleotides (ODN), activate dendritic cells and B cells in humans. However, naive B cells in humans, and follicular B cells in mice, in contrast to memory B cells and marginal zone (MZ) B cells, respond very poorly to stimulation with complex CpG-DNA ligands. As a result of TLR9 stimulation, B cells proliferate, upregulate co-stimulatory molecules and secrete antibodies and cytokines, e.g., IL-6 and IL-10. There is a concern that stimulation via TLR9 may cause a survival of immature autoreactive B cells, thus directly implicating TLR9 in the pathogenesis of systemic autoimmunity. Although mammalian DNA in general is non-immune stimulatory, under some conditions, DNA found in circulating immune complexes in lupus patients could stimulate autoreactive B cells and dendritic cells. Therefore, selectively blocking TLR9 pathway during early stages of lupus may be a promising tool for treating lupus. Over the last few years, we have developed a series of short ODNs that selectively block immune activation via the TLR9, but spare B cell activation via other signaling pathways. Recent structural modifications have resulted in the new class of these small DNA inhibitors (Class R) that show differential selectivity for various TLR9 expressing cells. The investigator hopes that the future use of these drugs in the treatment of human lupus may provide more disease-specific cure, avoiding unnecessary immunosuppression. [unreadable] [unreadable] In the Aim 1 of this grant, we investigate differing abilities of follicular and MZ-B cells to respond to complex CpG-DNA ligands. We study mechanisms responsible for CpG-DNA uptake into lymphoid cells, DNA trafficking and the role of the PI-3K family. We address the role of interferon priming in B cell activation. In Aim 2, we study the structural requirements and mechanism of action of recently developed class R-INH-ODNs. In Aim 3, we investigate whether these INH-ODNs can prevent or delay the onset of animal lupus, or decrease morbidity in mice with clinical lupus. Future extension of these studies to humans may lead to the design of novel therapeutic agents for human SLE. [unreadable] [unreadable] [unreadable]